1. Field of the Invention
The invention relates to endless belts for conveyors and, more particularly, to an endless belt having separately attached strips that are machined to form teeth.
2. Description of the Related Art
Conveyors transfer loads between two locations by carrying loads on the upper span of an endless belt. The belt is typically installed between a drive pulley that transfers torque to the belt and one or more idler pulleys. In certain environments, such as the food industry, cleanliness is extremely important. Thus it is common to use conveyor belts having a smooth, continuous surface that is made of thermoplastic material that can be maintained in a sanitary condition. Also common to the food industry is the use of thin, flexible belts. Thin belts are used for scale conveyors, where conveyed products are weighed while on the conveyor belt, because they are lightweight. Belts for scale conveyors must be lightweight so that the belt adds minimal load to the scale and must be under minimal tension so that the belt does not support any of the weight of the product. Conveyors must further be able to meet at various angles to transfer loads between two conveyors, but must be placed close together to minimize the gap between the conveyors at the transfer point. Thin, flexible conveyors are used in these applications where pulleys and nose bars with small radii are used because they allow a smaller gap between conveyors.
One type of thin, flexible belt is a pin belt, where the belt comprises a continuous surface on one side and holes on the other side adapted to engage pins on a drive pulley, much like the manner in which a dot-matrix printer advances paper. Because the belt has holes rather than teeth to engage the drive pulley, the pin belt can be made relatively thin and flexible. However, traditional pin belts are not ideal, because as the belt stretches due to the weight of conveyed loads, the pins and holes are no longer aligned with respect to one another and torque cannot properly be transferred to the belt through the pins and holes. Furthermore, a pin belt must be used with a drive pulley having pins, and cannot be modified for use with a toothed drive pulley.
An example of a toothed thermoplastic belt that alleviates the problems associated with belt stretching is disclosed in WO 2006/078890, which is incorporated herein by reference in its entirety. The thermoplastic belt disclosed is a low tension, direct drive toothed belt having a smooth, continuous surface on one side and a teeth extending the width of the belt on the other side that are adapted to engages grooves or sheaves on a drive sprocket. To account for belt stretching, the teeth are adapted to engage the sprocket at a sprocket pitch greater than the belt pitch. The teeth are integrally formed with the belt by machining teeth shapes into a piece of belt material. Because the teeth are formed by machining a piece of belt material, the teeth must be of the same material as the rest of the belt. Material lost by machining also adds to the cost of the belt. Furthermore, the belt cannot be used for scale conveyors and conveyors having small radii pulleys and nose bars because it is relatively thick and heavy.
Another example of a toothed thermoplastic belt that alleviates the problems associated with belt stretching is disclosed in U.S. Pat. No. 5,911,307, which is incorporated herein by reference in its entirety. The conveyor belt disclosed includes a flat belt having timing belt extending from one side of the belt to engage a pulley. The timing belt has preformed timing teeth and is laminated to the flat belt such that it is evenly spaced from the side edges of the flat belt. The belt does not require pretensioning, which by definition means stretching the belt.
Although the conveyor belt described above does not have stretching problems associated with a pin belt, and the material and application restraints associated with the belt from the '493 patent application, it cannot be used for nose bars because the timing belt would prevent the belt from freely moving around the nose bar. Furthermore, the timing teeth are preformed on the timing belt, requiring that the timing belt be robust enough to withstand normal handling. In other words, the timing belt must be thick in the spaces between teeth.